Reinforced sheet metal



, Patented .lune 8, 1948 REINFORCED SHEET METAL Richard S. Smith,Buffalo, N. Y., assignor, by mesne assignments, to ReconstructionFinance Corporation, New York the United States N. Y., a corporation ofApplication August 29, 1942, Serial No. 456,669 f l This inventionrelates to sheets 'of metal of various constituencies having improvedcharacteristics oi' strength and stiffness when compared with at sheetsof the same material lof equal unit weight.

The improved characteristics of stiffness and strength of the metalsheets of the present invention are attributable to a beneficialredistribution of the material with respect to neutral axes lying in aplane medially of the sheet. The particular application of theprinciples of the present invention which is set forth herein by way ofexample has reference to a metal sheet, and in general the formationsare intended to be produced by the cold rolling of hat sheets. In thegeneral field of metallic sheets the improvements of the presentinvention may be appliedA to both ferrous and non-ferrous metals. Thesuccessful attainment of the Vobjects of the present invention has beendemonstrated in the case of stainless,r alloy and carbon steels, andvarious aluminum alloys.

The use of plain corrugated sheets of metal, chiefly steel, has beenthoroughly explored and fairly widely used. This attempt atstrengthening steel is ineffective in all excepting very special cases,since its only effect is to stiffen the sheet when it is loaded as abeam with the corrugations running parallel to the direction of thebeam. If loaded at right angles to this direction a corrugated sheet hasvery much less stiffness than a plain sheet since the corrugationsmerely open up or flatten out. Likewise, a corrugated sheet has far lessresistance to buckling under compressive loads at right angles to thecorrugations and tensile forces in this direction do not meetsubstantial resistance until the sheet has y been stretched to asubstantially flat uncorrugated condition. Treating metal sheets bycorrugation methods increases the weight Iper unit of area as comparedwith the flat sheet, while treatment of sheets according to the presentinvention, by actual displacement of metal, de-4 teristics are impartedto the sheet, when compared with a fiat sheet of the same unit weightand material, and this is true regardless of the direction ofapplication of compressive buckling loads, tensile loads or iiexuralloads.' Strengthenl ing of a metal sheet in accordance with the prin- 4Claims. (Cl. 29,-180) ciples of the present invention may be eifected ina. varietyv of ways, as is` exemplified by the various alternative formsillustrated in the accompanying drawing, and described below. It is tobe understood that surface formations other than those illustrated indetail will occur to those skilled inthe art and the principles of thepresent invention are not to be limited otherwise than as defined in theappended claims.

`In the drawingsz" Fig. 1 is a transverse cross-sectional View of aportion of a sheet having formations in its opposite faces;

Fig. 2 is a similar view of a sheet having formations in one face only;

Fig. 3 is a view similar to Fig. 1 but with variant formations in itsopposite faces;

Fig` 4 is. an elevational view of the upper surface of the sheet of Fig.1; y

Fig. 5 is an elevational view of thelower surface of the sheet of Fig,1, and;

Fig. 6 is an elevational view of the upper surface of the sheet of Fig.3. l

Throughout the several figures of the drawing, like characters ofreference denote like parts and in Figs. 1, 4 and 5 the numeral I0designates y 'and disposed midway between adjacent ridges III, exceptingfor their regularly recurring sinuosity.

The angles of the` faces of the metal sheet between the ridges II' andthe groovesor valleys I2 are such that the height of eachridge II or itsdistance from the neutral axis of the crosssection of the sheet is aminimum when the adjacent sinuous grooves are closest I thereto andreaches a maximum when adjacent sinuous grooves are most remotetherefrom.l Reference to Fig. 4 shows that the grooves orvalleys I2 areso arranged that each adjacent pair either diverges or convergessimultaneously. l

Emcient production of a sheet having the surface formations of the.present invention is facilitated, and in fact the desired strength andstiffness characteristics are augmented, `by reversing the formations ofrthe reverse side of the sheet, shown in Fig. 5, as compared with theobverse side shown in Fig. 4. Stated generally, the underside of thelsheet of Fig. 1, as appears 3 from Fig. 5, has sinuous ridges designatedil and linear parallel grooves or valleys I5.

By reason of the relationship of the two faces of the sheet of Fig. 1, amaximum redistribution of the material of the sheet body I isaccomplished with a minimum of colning or cold-forging. The productionof the desired surface formations cannot be effected by a mere bendingof the sheet body; first, by reason of the sinuosity of the grooves onone face of the body and the ridges on the other, and second, by reasonof the desired sharp deiinitionof the crests of the ridges. This sharpdefinition contributes materially to the moment of inertia of thecrosssection, which is a direct measure of the resistance of thecross-section to bending.

Fig. 2 shows a sheet body 20'having in its upper surface formationsidentical with those of the Upper surface of Fig. 1 and accordingly likecharacters of reference have been applied thereto. The underside of thesheet body 20, designated 2|, is at. The ratios of strength andstiffness to unit weight will not be as high in the sheet of Fig. 2 asin the sheet of Fig. 1 but they will be substantially higher than in thecase of a plain sheet. Sheets of the kind shown in Fig. 2 may bedesirably employed in the formation of airfoils or other skin surfacingof aircraft. In such cases, obviously, the plain uninterrupted surfaceof the sheet will be exposed to the air stream to render the airfoil orother aircraft part aerodynamically emcient. The production of a sheetwith one plain surface may likewise be desired for purely aestheticreasons, or to facilitate decoration.

In Fig. 3 I have illustrated a form of surface treatment similar to thatof Fig. 1 but characterized chiefly by the fact that the ridges are lesssharply defined. I have found the crosssection of Fig. 3 to be moresatisfactory, from various standpoints, when applying the principles ofmy invention to heavier gauge metals.

In the upper or obverse face of the sheet of Fig. 3,

the body of which is designated 30, the crests are lineal and paralleland are designated 3l. Despite this parallelism and lineality, thecrests 3i ndulate in a vertical direction along their lengths. This isevidenced by the two elevations of the crests 3i appearing at the leftand right sides of the cross-section, Fig. 3.

In Fig. 6 the dot and dash construction lines indicate the crests 3i andthe shaded sinuous portions therebetween designate grooves or valleys32. Note that4 as shown in Fig. 3 the sinuous grooves'or valleys shownin Fig. 6 are at a condition of maximum divergence with respectjto thecentral crests 3l and are at a position of minimum spacing with respectto the ridges 3| lying on each side of the central ridge ofl Fig. 3. v

As in the case of Fig. 1, the under surface of sheet body 30 of Fig. 3is to some extent complementary to the upper surface. At its under sidethe sheet body'30 has lineal parallel grooves or valleys 34 and sinuousridges 35. The effect of this arrangement in the production of thevariation in height of the crests ,3l and the variation in the depths inthe grooves or the valleys 3,4 is` the same in principle as in the caseof Fig. 1.

It is by -virtue of this variation in crest and groove amplitude that across-section of any of the sheets, Figs. 1, 2 or 3, taken at rightangles 4 to those cross-sections, will similarly produce an undulatingcross-section. It is this fact that gives the sheet increased flexuralstrength with respect to cross-sections taken along the direction of thegeneral extent of the ridges and grooves.

Referring to preferred proportion of the formation, I have successfullydemonstrated the benets of the invention in cases where the distancebetween respective crests along a single ridge bore ratios varyingbetween 4 to 1 and 8 to 1 with respect to the lateral pitch of adjacentridges.

What is claimed is:

1. A reinforced structural sheet having longitudinal corrugationspresenting ridges at opposite sides thereof, the crests of the ridges atone side extending along straight parallel lines and tlie crests of theridges at the opposite sides being generally parallel but pursuing apredetermined regularly recurring sinuous course as viewedperpendicularly to said side of the sheet.

2. A structurally reinforced metallic sheet having a plurality ofadjacent longitudinal corrugations, the ridgeof each corrugationcomprising an undulating line as viewed in longitudinal cross-section,the crests of the undulating corrugations being staggered with respectto the crests of adjacent longitudinal corrugations, said corrugationshaving portions of maximum width at said crests and portions of minimumwidth at their nodes with adjacent staggered corrugations interfittinglaterally.

3. A reinforced structural sheet having a plurality of longitudinal,generally parallel ridges therein, said ridges having predeterminedregularly recurring variations in amplitude along their lengths, thevariations in amplitude being staggered with respect to the variationsin amplitude of ridges next adjacent thereto with the ridgesinteriitting laterally and all longitudinal cross sections through saidsheet produce undulating contours and the sheet is thus reinforcedagainst iiexure both transversely and longitudinally.

r 4. A reinforced structural sheet having a plurality of longitudinal.generally parallel ridges therein, said ridges having predeterminedregularlyrecurring variations in width along their lengths, thevariations in width being staggered with respect tothe variations inwidth of ridges next adjacent thereto with the ridges interilttinglaterally and all longitudinal cross sections through said sheet produceundulating contours and the sheet is thus reinforced against exure bothtransversely and longitudinally.

. RICHARD S. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATETS Dunajeif 'Man 4, 1941

